Balanced amplifier system



April 3o, 1949. R. RKREBS 2,399,441

BALANCED AMPLIFIER SYSTEM Filed April 16, 1945 VQQJ 4 67 R@ 4i@ 4W J 0.6'. SUP/u Y. t 30 ZZ Z5 Z5 '-Mynawl?? 3/ i Miri/ l z e *WFM- @5 4 o. c'. 50PM y 33 n INVENTOR :31994149 a, lc/w64,

' BY. H5474?? sap/z r E Patented Apr. 30, 1946 UNITED STATES PATENT OFFICE BALANCED Amm SYSTEM melma r. Krebs, lakewwa, ohm, assignmto Walter Soller, Cincinnati,- Ohio, and William H.

Y Woodin, Jr., Pasadena, Calif. y

Application April 1s, 194s, sei-iai No. 483,351

(ci. 11e-171) 4Clnims.

My invention relates broadly to electron tube circuits and more particularly to a balanced pentasl'id tube circuit.

One o! the objects oi my invention is to provide a circuit arrangement for a pentagrid tube circuit in whicha high degree of precision balance may be maintained in the electrical circuits for securing large magnification of feeble electrical currents.

Another object of my invention is to provide a circuit arrangement for a pentagrid electron tube including a'cathode, a space charge grid, a balancing grid, a screen grid, a control grid and an anode in which changes in emission current can be balanced or compensated independently of the balancing oi other parts ofthe circuit.

Still another object of my invention is to Provide a pentagrid tube circuit in which an adjustable balancing circuit is connected with the space charge grid and cathode for compensating or balancing the circuit against changes in emission independently of balancing arrangements associated with other portions of the pentagrid circuit.

A further object of my invention is to provide a. balancing circuit arrangement for a pentagrid tube which includesa cathode, a space charge grid, a balancing grid, a screen grid, a control grid and an anode wherein connection is arranged for the space charge grid to a point intermediate a pair of adiustable resistors disposed in the Yinput circuit to the tube where the resistors are so proportioned that the sum of the resistances and the ratio of the resistances may both be varied in such a way that ii positive regulation occurs the opposite condition will produce, negative regulation whereby adjustment may be made oi the value of the resistors to an intermediate condition of Vzero regulation.

Other and further objects of my invention reside in the arrangement of a resistance network in the input circuit to a pentode and a tap connection therefrom to the space charge grid oi the pentcde as set forth more fully in the specification hereinafter following by reference to the accompanying drawing in which:

Figure 1 diagrammatically illustrates one arrangement of balanced pentagrld tube circuit embodying my invention; and Fig. 2 illustrates a modied arrangement of pentagrid tube circuit embodying my invention. v

My invention is directed to a balanced pentagrid tube circuit having a high degree of stability independently of variations in voltage supplies to the circuits of the pentode and more particularly independent oi electron emission changes in the.-

pentode. I have successfully obtained voltage ampliiications of approximately. 200 employing the balanced pentagrid tube circuit of my invention. The particular feature of the circuit ot my 1invention is that changes in electron emission are balanced separately from the balancing of changes in the direct current power supply.

Referring to the drawing in more detail, the pentode is designated at llincludlng cathode Il which is heated by heater element l2, space charge grid i3, balancing grid Il, screen grid l5 serving as a shield for control grid i6 and anode il. The input circuit to the pentode has been indicated generally at I8 while the output circuit is shown generally at I9. For purposes of determining the condition of ballast, a galvanometer Z0 i s arranged in the output circuit. It will be understood that connections may extend parallel from the output system `of the pentagrild to another tube circuit or other current utilization circuit. The input circuit to the pentode is cozning for variations in electron emission from cathode ti.

The power supply to the heater I2 extends from 1 circuit 22 which includes series connected ad- Ajustable resistor R8 for controlling the temperature of heater element i2. The direct current power supply for the circuits of the pentode is represented generally at 23 connected between f the'cathode end of the pentagrid tube circuit at 2l and the anode end of the pentagrid tube circuit at 25; Adjustable resistor Re is arranged lin series between the direct current power supply cuit includes series connected individually adjustable resistors R3, RI, R5 and R6. A tap connection 2l between adjustable resistors R3 and R4 in. the circuit oi Fig. 1 leads to screen grid l5. A tap connection 2B between adjustable resistors R4 and R5 leads to the balancing grid I4. The tapped connection 29 between. adjustable resistors R5 and R8 leads through galvanometer 20 to anode Il. The balancing circuit is connected to ground as represented at 30 in both Figs. land 2.

In the arrangement shown in Fig. 1, the balancing of the pentagrid circuit is effected by means of control of potential on screen grid l5 which serves as a shield for control grid IS. In the arrangement shown in Fig. 2, the balancing of the pentagrid circuit is effected by controlling the potential on balancing grid IB, In both ar rangements the compensation for changes in electron emission is performed independently of the balancing of the pentagrid tube circuit as a whole.

The compensation for variations in electron emission is effected by adjustment of the resistance values o! adjustable resistors RI and R2. The balance for variations in electron emission depends upon both the total resistance RI+R2 and the ratio of these two resistances both being varied in such away that if positive regulation occurs the opposite condition will produce negative regulation. Resistors RI and R2 are independently varied until it is determined vunder what condition negative regulation occurs.

Then, noting both conditions or positive regulation and negative regulation, the value of the total resistance RI-l-RZ and a ratio of; Ri/Rz,

is selected such that zero regulation is obtained.

resistor R4 is varied until some balanced condition occurs `with a given deflection in the galvanometer 20 and then by changing resistor Rl to bring the galvanometer deection back to zero and repeating this operation until a balance of zero deiiection o1' the galvanometer is obtained. If the potential between the anode Il and the junction 29 between resistors R5 and R6 goes negative (indicated by the direction of the cur rent through the galvanometer 20) when the D. C. supply voltage increases then the potential of the rscreen grid I5 must be increased to counteract this and vice versa -when this potential goes positive. If necessary, resistors R3. R5 and R6 can be changed and the whole process lrepeated until satisfactory balance is obtained. The galvanometer 20 can be balanced against either a tap on the divider or a constant voltage with respect to ground.

I have found the balancing system of my invention highly eilicient in operation and have obtained voltage ampliflcations of approximately 200 using the circuit of my invention. I have found the independent circuit for compensating for electron emission highly efficient in pentagrid circuits which are subject to iiuctuations in heater potential and variations in thedirect current power supply. Such variations are extremely dlflicult to overcome and with the wider use of radio circuits in mobile units, are inherent where the voltage supplied to the radio'circuits is often dependent upon an over-charging condition o'f a generator due to speed of the' mobile unit. This is true independently of the fact that storage battery may normally be oated across such power supply lines as persistent over-charging from the generator 'often has detrimental .effects upon the circuits oi' the pentagrid tubes.`

fixed values may be substituted in the pentagrid tube circuits to meet an average condition of the variations which are to be expected in any given power supply system.

While I have described my inventionin certain of its preferred embodiments, I realize that modiiications may be made and no limitations upon screen grid, a control grid and an anode. a direct current supply source subject to variationin voltage, a plurality of means for impressing selected potentials on said electrodes from said supply source, an output circuit connected with said anode, an input circuit connected with said control grid and said cathode, an auxiliary circuit comprising a pair of independently adjustable resistors arranged in said input circuit, and a tap intermediate said resistors electrically connected with said space charge grid.

2. An electron tube circuit including a. multigrid tubeincluding a. cathode, a space charge grid, a control grid and an anode, an input circuit including said control grid and a circuit path to said cathode, a pair of separately adjustable resistors included in said path, a tap intermediate said separately adjustable resistors, a connection from said tap to said space charge grid, and anv output circuit connected with said anode.

3. A balanced electron tube system comprising a pentagrid electron tube having electrodes including a cathode, a heater element for said cathode subject to uctuating heater supply current, a space charge grid, a. balancing grid, a screen grid, a control grid and an anode, a direct cur- V rent supply source subject to variation in voltage,

a plurality of means for impressing selected potentials to said electrodes from said supply source, an output circuit connected with said anode, an input circuit connected with said control grid and said cathode, means for electrically balancing the circuits leading to said balancing grid, said screen grid and said anode, and independent means disposed in said input circuit comprising a pair of series connected separately adjustable impedances with an intermediate point therebetween connected with said space charge grid and said cathode for compensating for changes in emission from said cathode. y

4. A balanced electron tube system comprising a pentagrid electron tube having electrodes including a cathode, a heater element for said cathode subject to iluctuating heater supply current, a space charge grid, a balancing grid, a screen grid, a control grid and an anode, a direct current supply source subject to variation in voltage, a. plurality of means for impressing selected potentials on said electrodes from said supply source, an output circuit connected with said anode, an input circuit connected with said control grid and said cathode, a resistance network, circuit connections including said resistance network in said input circuit, said resistance network including a pair of independently adjustable resistors connected in series and a connection from a point intermediate said adjustable resistors in said resistance network to said space/charge grid for compensating for variations in electron emission from said cathode.

. RICHARD P. KREBS.4 

